﻿The relationship object shall not be used to include other spatial structure elements into a spatial structure element. The hierarchy of the spatial structure is defined using <em>IfcRelAggregates</em>. Exception: an <em>IfcSpace</em> can be referenced by another spatial structure element, in particular by an <em>IfcSpatialZone</em>.
<blockquote class="change-ifc2x4">IFC4 CHANGE&nbsp; The relaxation to allow <em>IfcSpace</em> has been included.
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